Beginning Python - From Novice to Professional

288 CHAPTER 13 ■ DATABASE SUPPORT
Table 13-3. Common Parameters of the connect Function
Parameter Name Description Optional?
dsn
Data source name. Specific meaning
database dependent.
user User name. Yes
password User password. Yes
host Host name. Yes
database Database name. Yes
No
You’ll see specific examples of using the connect function in the section “Getting Started”
later in this chapter, as well as in Chapter 26.
The connect function returns a connection object. This represents your current session
with the database. They support the methods shown in Table 13-4.
Table 13-4. Connection Object Methods
Method Name
close()
commit()
rollback()
cursor()
Description
Close the connection. Connection object and its cursors are now unusable.
Commit pending transactions, if supported. Otherwise do nothing.
Roll back pending transactions. (May not be available.)
Return a cursor object for the connection.
The rollback function may not be available, because not all databases support transactions.
(Transactions are just sequences of actions.) If it exists, it will “undo” any transactions
that have not been committed. The commit function is always available, but if the database
doesn’t support transactions, it doesn’t actually do anything. If you close a connection and
there are still transactions that have not been committed, they will implicitly be rolled back—
but only if the database supports rollbacks! So if you don’t want to rely on this, you should
always commit before you close your connection. If you commit, you probably don’t have to
worry too much about closing your connection; it’s automatically closed when it’s garbage
collected. If you want to be on the safe side, though, a call to close won’t cost you that many
keystrokes . . .
The cursor function leads us to another topic: cursor objects. You use cursors to execute
SQL queries and to examine the results. Cursors support more methods than connections, and
probably will be quite a bit more prominent in your programs. Table 13-5 gives an overview of
the cursor methods, and Table 13-6 gives an overview of the attributes.